Re: [paho-dev] List * handles passed as NULL in MQTTAsync.c
Sure this was taken directly from one of the examples (and modified for ssl) it was exhibiting the same issue:
int main(int argc, char* argv)
MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
MQTTClient_SSLOptions sslOpts = MQTTClient_SSLOptions_initializer;
conn_opts.ssl = &sslOpts;
sslOpts.trustStore = "/etc/ssl/certs/StartCom_Certification_Authority.pem";
MQTTClient_create(&client, ADDRESS, "serial123", MQTTCLIENT_PERSISTENCE_NONE, NULL);
conn_opts.keepAliveInterval = 20;
conn_opts.cleansession = 1;
MQTTClient_setCallbacks(client, NULL, connlost, msgarrvd, delivered);
if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
printf("Failed to connect, return code %d\n", rc);
printf("Subscribing to topic %s as %s\nfor QoS %d\n\n"
"Press Q<Enter> to quit\n\n", argv,conn_opts.username, QOS);
MQTTClient_subscribe(client, argv, QOS);
ch = getchar();
} while(ch!='Q' && ch != 'q');
From: paho-dev-bounces@xxxxxxxxxxx [paho-dev-bounces@xxxxxxxxxxx] on behalf of Ian Craggs [icraggs@xxxxxxxxxxxxxxxxxxxxxxx]
Sent: Friday, April 25, 2014 8:08 AM
Subject: Re: [paho-dev] List * handles passed as NULL in MQTTAsync.c
can I have a snippet of your application code to show how you are using
the client library?
On 04/24/2014 11:36 PM, Jimmy Johnson wrote:
> Hi Ian,
> I found another possible bug in the C code, and created a possible fix. Here is what I found:
> My client was making a call to MQTTClient_create() in MQTTClient.c which initalizes it's static instance of the "handles" pointer. When the client actually published a message it was calling an instance of Protocol_processPublication which is located in MQTTAsync.c and using the instance of the static "handles" pointer in that file which had never been initalized since I had originally call MQTTClient_create() in MQTTClient.c to set up the client. This caused a segfault when it hit the ListFindItem method with handles set as NULL.
> Here is my stack trace:
> #0 0x4002e550 in ListFindItem (aList=0x0, content=0x3c68c,
> callback=0x40035b48 <clientStructCompare>) at src/LinkedList.c:154
> #1 0x40035ff0 in Protocol_processPublication (publish=0x306bc,
> client=0x3c68c) at src/MQTTAsync.c:1809
> #2 0x400403e8 in MQTTProtocol_handlePublishes (pack=0x306bc, sock=6)
> at src/MQTTProtocolClient.c:275
> #3 0x400e5e2c in MQTTClient_cycle (sock=0x41616db4, timeout=1000,
> rc=0x41616db8) at src/MQTTClient.c:1508
> #4 0x400e24c4 in MQTTClient_run (n=0x3c4fc) at src/MQTTClient.c:483
> #5 0x40189910 in start_thread () from /lib/libpthread.so.0
> #6 0x405913ec in clone () from /lib/libc.so.6
> You can see that aList which is a List * is being passed in as NULL (0x0) to ListFindItem after being called from MQTTAsync.c
> My fix was to add a parameter to Protocol_processPublication called handles for both MQTTAsync.c and MQTTClient.c files.
> void Protocol_processPublication(Publish* publish, Clients* client)
> void Protocol_processPublication(Publish* publish, Clients* client, List * handles)
> I then re factored calling methods to include their instance of the handle when making this call. It seemed to fix everything since the call is no longer relying on a global variable. Oddly enough I did not see this issue when I was compiling and testing under Ubuntu 12.04 on my laptop. It only started happening only when I cross compiled to my arm platform. Do you think it will cause any issues? I am using the library with c++, I don't know if that would make a difference. I know the docs say that a synchronous client becomes asynchronous when you create callbacks for it, but it doesn't seem to initialize the asynchronous part of the code.
> Thanks for any insight you might have.
> paho-dev mailing list
icraggs@xxxxxxxxxx IBM United Kingdom
Committer on Paho, Mosquitto
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